Company X is customer of operator Z and has a subscription for voice and data with 10 SIM cards. The company also decides to subscribe to the private numbering plan feature of operator Z. A certain corporate phone number is assigned to company X, e.g. +43 676 88888 xx (with xx being the extensions of the users), and they can freely choose the extensions for up to 100 SIM cards. Initially company X take the existing 10 SIM cards (with the existing MSISDNs) and integrate them into the private numbering plan by assigning the extensions 11 to 20 to these cards via a web portal. This is not a permanent assignment, the extensions can be changed easily any time, old SIMs can be deleted from the private numbering plan and new ones can be integrated whenever necessary. Special privileges or restrictions can be chosen on a per SIM basis via the portal and special tariffs apply. The CEO of company X calls a customer. The customer's phone displays the corporate number + extension of the CEO as CLI. After a while the customer decides to call back the CEO and uses the corporate number + extension as MSISDN. Later they also exchange some short messages, again the corporate number + extension of the CEO is used as sender's MSISDN. For all these calls and short messages operator Z is able to collect charging records containing the corporate number + extension. The CEO also uses her smart phone to establish PS connections to browse the internet and to access the intranet via the operator's gateway. The corporate number + extension is used for authentication and authorisation in the company's intranet and its web applications. Charging for PS connections by operator Z is also based on this number. In general the users in company X are not aware of their "real" underlying MSISDNs in the system, they only see the corporate number + their extension and there is no need for them to know the underlying MSISDN.